linux-kernel - Re: [PATCH v2 1/2] vfio/iommu_type1: Populate full dirty when detach non-pinned group

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Message-ID: <20210115110144.61e3c843@omen.home.shazbot.org>
Date:   Fri, 15 Jan 2021 11:01:44 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH v2 1/2] vfio/iommu_type1: Populate full dirty when
 detach non-pinned group

On Fri, 15 Jan 2021 17:26:42 +0800
Keqian Zhu <zhukeqian1@...wei.com> wrote:

> If a group with non-pinned-page dirty scope is detached with dirty
> logging enabled, we should fully populate the dirty bitmaps at the
> time it's removed since we don't know the extent of its previous DMA,
> nor will the group be present to trigger the full bitmap when the user
> retrieves the dirty bitmap.
> 
> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
> Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 0b4dedaa9128..4e82b9a3440f 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -236,6 +236,19 @@ static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
>  	}
>  }
>  
> +static void vfio_iommu_populate_bitmap_full(struct vfio_iommu *iommu)
> +{
> +	struct rb_node *n;
> +	unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> +
> +	for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
> +		struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> +
> +		if (dma->iommu_mapped)
> +			bitmap_set(dma->bitmap, 0, dma->size >> pgshift);
> +	}
> +}
> +
>  static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu, size_t pgsize)
>  {
>  	struct rb_node *n;
> @@ -2415,8 +2428,11 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>  	 * Removal of a group without dirty tracking may allow the iommu scope
>  	 * to be promoted.
>  	 */
> -	if (update_dirty_scope)
> +	if (update_dirty_scope) {
>  		update_pinned_page_dirty_scope(iommu);
> +		if (iommu->dirty_page_tracking)
> +			vfio_iommu_populate_bitmap_full(iommu);
> +	}
>  	mutex_unlock(&iommu->lock);
>  }
>  

This doesn't do the right thing.  This marks the bitmap dirty if:

 * The detached group dirty scope was not limited to pinned pages

 AND

 * Dirty tracking is enabled

 AND

 * The vfio_dma is *currently* (ie. after the detach) iommu_mapped

We need to mark the bitmap dirty based on whether the vfio_dma *was*
iommu_mapped by the group that is now detached.  Thanks,

Alex